33. Pterygium - The GEC-ESTRO Handbook of Brachytherapy

Pterygium

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THE GEC ESTROHANDBOOKOF BRACHYTHERAPY | Part II Clinical Practice Version 1 - 01/03/2023

11. MONITORING

bed with an additional safety margin of 1mm of the cornea and 3-4 mm of the eye limbus. As shown in figure 3 it is important to consider that the applicator consists of a central radioactive area and an inactive rim zone. In some cases where the surgical resection area is too large, then two applications should be used usually overlapping each other to a limited extent. If faced with a large circular applicator and healthy cornea overlying, an individual protector can be made of thin lead foil to conserve the healthy part of cornea. Care is needed considering the thickness of foils allowing for possible X-ray contamination. A thicker layer may produce soft X-rays.The delivered dose to the lens with strontium-90 applicators is less than 5%, consistent with the very rapid dose fall-off near the strontium-90 applicator (figure 5). Several attempts to use radiotherapy to treat pterygiumhave been performed during the last century [19] and several authors have tried to identify the optimal regimen in terms of timing, total dose and fractionation [20]. The first fraction should be delivered a few hours (less than 24 hours) after the excision. Currently, there is a huge variety of postoperative dose and fractionation schemes, ranging from 20 Gy as single dose to 60 Gy in 6 fractions [6]. The largest and latest series available in the literature mainly used 30-35 Gy in 3, 5 or 7 fractions. A randomized postoperative dose finding study showed no significant differences between 30 Gy in three fractions over 15 days compared to 40 Gy in 4 fractions over 22 days prescribed to the surface of the eye for primary lesions in terms of local control rates. No differences in terms of acute and late complications were noted. A comprehensive report of doses and fractionations used in literature is reported in table 1. 10. DOSE, DOSE RATE, FRACTIONATION

During the application tolerance is quite acceptable because of the local anaesthesia. It is important to carefully keep the correct position of the applicator during the radiation time. In applications lasting for several minutes it is advised to stop halfway, to relax a while and to check correct positioning. During the days following irradiation a local reaction with redness, tear formation and sometimes minor conjunctivitis is noted and may last for 4 - 6 weeks following the treatment. A topical ointment application is prescribed with 3-4 days local antibiotics and corticosteroids until inflammation has disappeared (usually within one week).

12. RESULTS

A comprehensive literature review collected data regarding over 6000 lesions treated by radiotherapy. The results of combined resection and postoperative beta irradiation are reported in table 1. It is important to underline that prospective randomized trials are scarce andmost of the clinical evidence available from retrospective studies. It was reported that eighty percent of recurrences developed within 3 years after treatment [21].

13. ADVERSE EVENTS

Among the most common adverse effects are visual disturbances (4.2%) and congestion (2.5%); less frequently encountered adverse events include scleromalacia (1,2%), adhesion of eye lids (1%), scleral ulcer (1%), cataract (0.8%), scleral thinning (0.8%) and ulceration (0.5%). Generally, ocular morbidities, in particular scleral necrosis, are more frequent and more severe if radiotherapy is performed in the presence of a conjunctival defect [36].